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The U.S. Department of Energy
Computer Incident Advisory Center
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INFORMATION BULLETIN
Cisco Multiple Vulnerabilities in CBOS
May 23, 2001 01:00 GMT Number L-086
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PROBLEM: TCP Sequence Prediction, echo request denial of service
vulnerabilities, NVRAM password stored cleartext.
PLATFORM: Cisco 600 series routers (CBOS Software)
DAMAGE: Ranges from denial of service to unauthorized access and
disclosure, depending on vulnerability exploited.
SOLUTION: Upgrade to releases not vulnerable, as described below.
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VULNERABILITY MEDIUM. There are multiple vulnerabilities described, ranging
ASSESSMENT: from temporary denial of service, to compromise of the router.
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[****** Start Cisco Advisory ******]
Cisco Security Advisory: More multiple vulnerabilities in CBOS
Revision 1.0
For public release 2001 May 22 08:00 (GMT -0800)
______________________________________________________________________
Summary
Multiple vulnerabilities have been identified and fixed in CBOS, an
operating system for the Cisco 600 family of routers.
* Cisco CBOS Software contains a flaw that permits the successful
prediction of TCP Initial Sequence Numbers. It only affects the
security of TCP connections that originate or terminate on the
affected Cisco device itself; it does not apply to TCP traffic
forwarded through the affected device in transit between two other
hosts.
This vulnerability is documented as Cisco bug ID CSCds16078.
* A Cisco 600 router may stop passing the traffic and responding to
the console when an ECHO REQUEST packet with the record route
option is routed through it.
This vulnerability is documented as Cisco bug ID CSCds30150.
* Passwords, exec and enable, are stored in the cleartext in the
NVRAM.
This vulnerability is documented as Cisco bug ID CSCdt04882.
* When multiple, large ECHO REPLY packets are routed through an
affected Cisco 600 router, it will enter the ROMMON mode and stop
passing any further traffic.
This vulnerability is documented as Cisco bug ID CSCds74567.
The following releases of CBOS are containing all of mentioned
vulnerabilities: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a, 2.3,
2.3.2, 2.3.5, 2.3.7 and 2.3.8.
These vulnerabilities are fixed in the following CBOS releases: 2.3.9,
2.4.1 and 2.4.2. Customers are urged to upgrade to releases that are
not vulnerable as shown in detail in the section Software Versions and
Fixes below.
This advisory is available at the
http://www.cisco.com/warp/public/707/CBOS-multiple2-pub.html.
Affected Products
The affected models are: 627, 633, 673, 675, 675E, 677, 677i and 678.
These models are vulnerable if they run any of the following, or
earlier, CBOS releases: 2.0.1, 2.1.0, 2.1.0a, 2.2.0, 2.2.1, 2.2.1a,
2.3, 2.3.2, 2.3.5, 2.3.7 and 2.3.8.
No other releases of CBOS software are affected by these
vulnerabilities. No other Cisco products are affected by these
vulnerabilities.
These vulnerabilities are fixed in the following CBOS releases: 2.3.9,
2.4.1 and 2.4.2.
Details
CSCds16078
See also
http://www.cisco.com/warp/public/707/ios-tcp-isn-random-pub.
shtml
TCP sequence numbers are 32-bit integers in the circular range
of 0 to 4,294,967,295. The host devices at both ends of a TCP
connection exchange an Initial Sequence Number (ISN) selected
at random from that range as part of the setup of a new TCP
connection.
This method provides reasonably good protection against
accidental receipt of unintended data. However, to guard
against malicious use, it should not be possible for an
attacker to infer a particular number in the sequence. If the
initial sequence number is not chosen randomly or if it is
incremented in a non-random manner between the initialization
of subsequent TCP sessions, then it is possible, with varying
degrees of success, to forge one half of a TCP connection with
another host in order to gain access to that host, or hijack an
existing connection between two hosts in order to compromise
the contents of the TCP connection. To guard against such
compromises, ISNs should be generated as randomly as possible.
CSCds30150
By sending ICMP ECHO REQUEST packets (ping) with the IP Record
Route option set it is possible to freeze a Cisco 600 router.
This can be done either by sending the specially crafted packet
or by specifying the "-r" option on the most ping programs.
The packet should not be destined to a router itself.
CSCdt04882
The exec and enable passwords are stored in the cleartext in
NVRAM. Similarly, they are also stored in the cleartext in the
configuration file if one is stored on a computer. Anyone who
is in a position to see a router's configuration, either
directly from the device or in the file on a computer, can
learn the passwords.
This vulnerability is corrected by storing only an MD5 hash of
the password in both NVRAM and in the configuration file, and
the plaintext password itself is never retained.
CSCds74567
When multiple ICMP ECHO REPLY packets, non standard size, are
passed through the affected device the device will stop passing
any further traffic. Packets must be larger than the usual size
(64 bytes) but that can be easily accomplished either by
crafting packets or by adjusting the response size, either via
command line or by modifying the program source.
Impact
CSCds16078
Forged packets can be injected into a network from a location
outside its boundary so that they are trusted as authentic by
the receiving host, thus resulting in a failure of integrity.
Such packets could be crafted to gain access or make some other
modification to the receiving system in order to attain some
goal, such as gaining unauthorized interactive access to a
system or compromising stored data. From a position within the
network where it is possible to receive the return traffic (but
not necessarily in a position that is directly in the traffic
path), a greater range of violations is possible. For example,
the contents of a message could be diverted, modified, and then
returned to the traffic flow again, causing a failure of
integrity and a possible failure of confidentiality. NOTE: Any
compromise using this vulnerability is only possible for TCP
sessions that originate or terminate on the affected Cisco
device itself. It does not apply to TCP traffic that is merely
forwarded through the device.
CSCds30150
It is possible to cause the Denial-of-Service.
CSCdt04882
Anyone who is in a position to see a router's configuration,
either directly from the device or in the file on a computer,
can learn the exec and enable passwords. Armed with that
knowledge, an attacker can log into the device and change the
router's configuration.
This vulnerability can be even more dangerous if the ISP is
using the same passwords for all of the devices which it
manages. Such practice, using the same passwords for multiple
devices, is strongly discouraged.
CSCds74567
It is possible to cause the Denial-of-Service to many affected
devices.
Software Versions and Fixes
The following table summarizes the CBOS software releases affected by
the vulnerabilities described in this notice and scheduled dates on
which the earliest corresponding fixed releases will be available.
+===========+================+=====================================+
| | | |
| Release | Description or | Availability of Repaired Releases |
| | Platform |=====================================+
| | | General Availability (GA) |
+===========+================+=====================================+
| All | All platforms | 2.3.9 |
| releases | | 2001-Mart-19 |
+-----------+----------------+-------------------------------------+
| All | All platforms | 2.4.1 |
| releases | | 2000-December-11 |
+-----------+----------------+-------------------------------------+
| All | All platforms | 2.4.2 |
| releases | | 2001-May-14 |
+===========+================+=====================================+
Obtaining Fixed Software
Cisco is offering free software upgrades to eliminate this
vulnerability for all affected customers.
Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained via the point-of-sale or, if they posses a Cisco
Connection Online account, they can download it from the Software
Center on Cisco's Worldwide Web site at http://www.cisco.com.
Customers without contracts should get their upgrades by contacting
the Cisco Technical Assistance Center (TAC). TAC contacts are as
follows:
* +1 800 553 2447 (toll-free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac@cisco.com
Give the URL of this notice as evidence of your entitlement to a
free upgrade. Free upgrades for non-contract customers must be
requested through the TAC.
Please do not contact either "psirt@cisco.com" or
"security-alert@cisco.com" for software upgrades.
Workarounds
CSCds16078
There is no workaround.
CSCds30150
There is no workaround.
CSCdt04882
There is no workaround.
CSCds74567
There is no workaround.
Exploitation and Public Announcements
Vulnerabilitiy CSCds30150 has been made public on VULN-DEV list.
Altough we have not seen public discussion of vulnerability CSCdt04882
we understand that it is commonly known among users.
Vulnerability CSCds74567 has been reported to us by a customer.
Status of This Notice: FINAL
This is a final notice. Although Cisco cannot guarantee the accuracy
of all statements in this notice, all of the facts have been checked
to the best of our ability. Cisco does not anticipate issuing updated
versions of this notice unless there is some material change in the
facts. Should there be a significant change in the facts, Cisco may
update this notice.
Distribution
This notice will be posted on Cisco's Worldwide Web site at
http://www.cisco.com/warp/public/707/CBOS-multiple2-pub.html. In
addition to Worldwide Web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients:
* cust-security-announce@cisco.com
* bugtraq@securityfocus.com
* first-teams@first.org (includes CERT/CC)
* cisco@spot.colorado.edu
* comp.dcom.sys.cisco
* firewalls@lists.gnac.com
* Various internal Cisco mailing lists
Future updates of this notice, if any, will be placed on Cisco's
Worldwide Web server, but may or may not be actively announced on
mailing lists or newsgroups. Users concerned about this problem are
encouraged to check the URL given above for any updates.
Revision History
Revision 1.0 2001-May-22 08:00 GMT-0800 Public release
Cisco Security Procedures
Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's Worldwide Web site at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml.
This includes instructions for press inquiries regarding Cisco
security notices.
_________________________________________________________________
This notice is Copyright 2000 by Cisco Systems, Inc. This notice may
be redistributed freely after the release date given at the top of the
text, provided that redistributed copies are complete and unmodified,
and include all date and version information.
_________________________________________________________________
[****** End Cisco Advisory ******]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of Cisco for the
information contained in this bulletin.
_______________________________________________________________________________
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